Manufacture of cellulose esters



Patented Nov. 21, 1933 MANUFACTURE OF oELLULosE E STERS I Henry Dreyfus, London, England No Drawing. Application November 24, 1928,

Serial No. 321,752, and in Great Britain Deoember 17, 1927 4 Claims. (Cl. 260-101) This invention relates'to a new or improved process for the manufacture of cellulose acetates and cellulose esters of higher homologues of acetic acid, for example propionic acid or butyric acid.

According to the present invention cellulose esters are produced by subjecting cellulosic materials to a pretreatment with organic acids, particularly lower aliphatic acids such as formic or acetic acid, and then to esterification by means of fatty acid anhydrides, particularly acetic anhydride, inpresence of one or more chlorides or other halides of antimony, arsenic or phosphorus, and in presence or absence of hydrochloric or otherhydrohalic acid. The halides of phosphorus, antimony and arsenic are hereinafter in the claims referred to as halides of congeners of nitrogen.

Some of the-halides of these elements, notably antimony trichloride and phosphoruspentaand oxy-chlorides, have previously been proposed for use as condensing agents in the acetylation of cellulose but it is found thatcomplete acetylation is only possible at temperatures at which substantial degradation of the cellulose takes place and this being so the high viscosity acetates considered essential in modern commercial practice are unobtainable by the proposed processes.

. I have found that with antimony pentachloride .or phosphorus pentachloride or mixtures thereof very valuable esters may be obtained if the cellu losic materials be pretreated with organic acids and that still better results are obtainable if the said halides be employed in conjunction with hyof. the. acids, the vapours being employed alone drochloric acid. I have also found that by employing other halides of phosphorus orantimony orv halides of arsenic wholly or partly in" place of the anti-' mony and phosphorus 'penta'chloridesand, if an acid be used, hydrobromic or hydriodic acid wholly or partly in place ofv the hydrochloric acid very good results may be obtained, provided that the cellulosic materials-be pretreated with organic acids.

. With low proportions of the halide and of the acid (if used) the acetylation or other esterifica- .tion will take a considerable time if conducted at temperatures not liable to cause degradation of the cellulose and from the point of view of obtaining a good product in .a reasonably short time, it is'preferred to employ quantities of halide of over 5% calculated on the cellulose and'preferably quantities of 10-25%. When using an acid the preferred quantities area-15% of halide and of acid. The proportion of halide may be increased to 30% or more, though amounts of fied products and of cellulose ethers.

over 50% are not advisable. Similarly the amountof acid may be increased to more than 15%. V

As initial materials for acetylation or esterification cottonor other celluloses or near conversion products thereof or other cellulosic materials may be employed. -Wood pulps, such as sulphite' pulp, soda pulp, sulphate pulp or mechanical wood pulps, or bamboo,.esparto or other materials containing 'encrusting matter and from which the lignin; pentosan, resin and like constituents have been substantially removed, may be employed, but are preferably subjected, prior to the treatment withorganic'acids, to'an alkaline purifying treatment as described in my U. S. 70 Patent 1;7l1,110 issued'April 30," 1929. For example the alkaline purifying treatment may be performed'with caustic alkali of low concentration, such as 3% or under, with heating or boiling, or with caustic alkali of high concentration, such as 5-;10% or more, in the cold or with only slightjheating. The invention further contemplates the acetylationpr other esterification of already esteri- The pretreatment of the cellulosic materials with organic acidsmaybe carried out in any suitable manner. .Thus,'"for example, they may be .pretreated with the concentrated or dilute acids,

particularly formic or acetic acid, as described in my French specification No. 565,654 or, as described in my U. S. patent application Serial No.

66,103 filed 31st October 1925, with the vapours reacts with acetic' 'anhydride. I have found that the best resultsiare obtained if the cellulosic material be pretreated with formic acid or with a mixture of formic acid, and acetic acid.

In order to avoid degradation of the cellulose molecule the acetylation or other esterification is preferably carried out at temperatures not exceeding 50 C. The most valuable esters are'obtained if the esterification is performed at low temperatures, for example below atmospheric,

e. g. 10 C. to 5 or 0 C. or lower, at ordinary temperatures or at temperatures, such as to C. not substantially above atmospheric.

The esterification may be performed in presence of a solvent for the cellulose ester produced; acetic acid is particularly suitable in the case of manufacturing cellulose acetates but any other suitable solvents (or solvent mixtures) of the cellulose acetates or other cellulose esters may be employed. The acetic acid or equivalent solvent or solvent mixture may be present in any desired quantity, such as 4 to 6 times the Weight of the cellulose or near conversion product, but cellulose acetates or other cellulose esters of specially high viscosity can be obtained if the acetic acid or equivalent solvent or solvent mixture is present in an amount greater than six times, for example 8 to 20 times or more the weight of the cellulose or conversion product as hereinafter referred to. Small quantitiessuch for instance as to 10% reckonedon'the weight of the cellulose-of more powerful organic solvents for cellulose acetates or the other cellulose esters, such for example as ethylidene diacetate, lactic acid or its acetyl derivatives, may be added to the acetic acid or other solvent or solvent mixturaas indicated in my U. S. Patent 1,711,111 issued April 30, 1929, or such more powerful solvents may be produced in the acetylation or esterification solution, for example by addition of acetaldehyde to produce ethylidene diacetate by reaction with the acetic 'anhydride in the case of producing cellulose acetates.

' In a previous U. S. Patent 1,708,787 issued April 9, 1929, I have indicated that cellulose acetates of specially high viscosity characteristicscan be obtained by conducting the acetylation in presence of acetic acid or equivalent solvents or solvent mixtures in an amount greater than six times, for example 8 to 20 times or more, the weight of the cellulose or cellulose conversion product used. With the present invention likewise the acetylation or esterification may with advantagefor the production of very highly viscous cellulose acetates or other cellulose esters, be conducted in presence of similar large amounts of acetic acid or equivalent solvents or solvent mixtures, for example other fatty acids higher'than acetic acid, or other suitable acids, or liquids such as chloroform, tetrachlorethane, ormixtures of such solvents or liquids.

.Alternatively the acetylation. or esterification may be performed in suspension in liquid diluents,

such for example as benzene or toluene.v The esterification in suspension may, for instance, be conducted on the lines indicated in my French Patent No. 432,046 and its patents of addition Nos. 15,933 and 16,316. If desired solvents, for example acetic acid, maybe present in addition to the liquid diluents. Furthermore acetic acid or equivalent solvent may again be used in quantities over six times the weight of the cellulose, for example 8-20 times or more, to obtain cellulose esters of high viscosity as described in my U. S. Patent 1,708,787 issued April 9, 1929. In allsuch cases of using. solvents in addition to liquid diluents, the

liquid diluent should be present in sumcient quantity to prevent solution of the cellulose acetate or other cellulose ester produced.

As a further modification the esterification may be conducted substantially in absence of .liquid solvents or diluents by employing vapours of acetic anhydride or other esterifying agent as described in my U. S. patent application Serial No. 72,403 filed 30th November 1925.

Fibres, fabrics or the like, for example of cotton or other natural cellulosic materials, or of viscose artificial silk or of other regenerated cellulosic artificial fibres, may be acetylated or 100 parts of cotton cellulose are pretreated with formic acid, for example by treatment with 500 to 1000 parts or more of formic acid of about 85% strength, allowing to stand for some hours in the cold and hydro-extracting or by impregnating with about 15 parts of formic acid of 75-85% strength and then allowing to stand for about 8-12 hours at ordinary temperature. If desired the material may then be washed to remove the formic acid and centrifuged or dried. The parts of pretreated material are introduced in the acetylator into a mixture of 600 100 parts of acetic anhydride, 600 parts of acetic-acid and 25 parts of antimony penta-chloride, and the mass is constantly mixed or stirred during the reaction, which is conducted at atmospheric temperature. The acetylation proceeds smoothly and a clear colourless solution is obtained. The solution may either be utilized directly or the cellulose acetate precipitated and redissolved or worked up in any desired manner.

Example 2 no 100 parts of cotton cellulose are pretreated and then subjected to acetylation as described in Example 1 with the exception that instead of 25 parts of antimony pentachloride 10 parts of 11.5 antimony pentachloride and 10 parts of hydrochloric acid are employed. Similar results are obtained. 1

Example 3 100 parts of cotton cellulose are introduced into a mixture'of 500 parts of formic acid of 85% strength and 500 parts of glacial acetic acid, allowed to stand for some hours in the cold and are then hydro-extracted and dried. The pretreated material is introduced in the acetylator into a mixture of 800 parts of acetic acid, 300 parts of acetic anhydride and 20 parts of phosphorous penta-chloride. The reaction carried 7 out in the cold with constant mixing or stirring. A clear colourless solution is obtained of a cellulose acetate of very high viscosity.

In a similar manner other halides of antimony or phosphorus or halides of arsenic may be used to effect the acetylation and furthermore by employing the appropriate anhydride or anhydrides other cellulose esters or mixed esters may be obtained.

The cellulose acetates or other cellulose esters resulting from acetylation or other esterification according to the invention may be used in their esterification solutions or in solutions of the primary esterification products for the production of artificial silks, films etc. or they may be sub jected to secondary treatments or reactions for 3145 the purpose of changing their solubilities. The secondary treatments or reactions may be carried out in the primary esterification solutions or suspensions preferably without neutralizing 7 any acid present and. after destroying if necesproduction of artificial sary any remaining anhydride by the addition of water or other anhydride-destroying' agents, (such for instance as hydroxyl derivatives, .oxy acids, for instance lactic acid, alcohols etc.)-. If desired hydrochloric or other hydrohalide'acid may be added to accelerate the reaction. Alternatively the esters either precipitated from the primary esterification solutions or those obtained other than in solution, may be dissolved or suspended and then subjected to the secondary treatments. The secondary treatments or reactions may be carried out with or without addition of inorganic or organic acids, acid salts or other suitable agents for promoting the secondary treatment or reaction, the treatment in any case being stopped when the required solubility has been reached.

' For the further treatments or reactions one should first destroy any remaining acetic anhydride or other esterifying anhydride that may remain in the esterification solution or suspension or in the primary ester, by adding water or other anhydride-destroying agents to the esterification solution or to the solutions or suspensions of the primary ester.

While the secondary or further treatment of the primary esterification products may with advantage be conducted at ordinary or moderate temperatures, one may if desired quicken the reaction by heating up to relatively high or high temperatures, even up to or 100 C. but in such cases the presence of free mineral acids is preferably avoided; i

The secondary or further treatments of the primary esterification products will be stopped when the particular solubility desired is reached.

An important advantage of the present invention is the fact that the cellulose-acetates or other esters can be employed in their primary esterification solutions in their different stages or phases of acetylation or esterifi'cation, for the silks and the like, films, celluloid substitutes or other thermoplastic masses or articles, etc.

Further the invention permits of obtaining cellulose esters of high quality which are soluble in acetone or in very low boiling solvents, for instance methyl formate, acetaldehyde, formaldehyde etc. Also suitable high boiling solvents or plasticizing or softening agents can be readily incorporated with them or their solutions in volatile solvents and/ or very low boiling solvents.

The new cellulose acetates or other esters, either in their primary esterification solutions and with or without secondary treatments or as primary or secondary esters in solution in suit' able solvents, for example acetone, ethyl alcoholacetone, methyl alcohol-acetone, or the very low boiling solvents referred to above or in mixtures of such'solvents may be employed for the prorelatively low concentration for instance duction of artificial silks or fibres, films etc. For

either wet or dry-spinning processes the esters may be employed in the form of solutions of or of medium concentration, for example 10-20%, or of high concentration containing over 20%, e. g. 25-30% or more.

As examples of suitable precipitating liquids for use in wet-spinning processes the following may be mentioned;-alcohols, for example methyl and ethyl alcohols and their homologues; coal tar, petroleum or other hydrocarbons, for instance benzene, toluene and their homologues,

gasoline, kerosene and the like; and aqueous liquids containing, for example, suitable proportions of mineral acids, e. g. sulphuric acid, of acid salts, e. g. bisulphates, of neutral salts, e. g. sodium, potassium, calcium or magnesium chloride, or, as described in prior U. S. Patents Nos.

1,465,994 and 1,467,493, of thiocyanates, zinc chloride, acetone, diacetone alcohol, alcohol, acetic acid, formic acid or other salts or substances having a latent solventpower for the cellulose acetate or other ester. cipitating liquids may, if desired, be incorporated in suitable proportions in the spinnng solutons prior to extrusion.

For the production of artificial silks or fibres, films etc. as well as for the production of thermoplastic masses, articles and the like, placticizing or softening agents or high boiling solvents may be incorporated in the esters or in their solutions.

What I claim and desire to secure by Letters Patent is:-

1. Process for the production of cellulose acetate, comprising pretreating cellulose with formic acid and acetylating them by means of acetic anhydride in presence of pentachlorides of congeners of nitrogen and in presence of hydrochloric acid each in a proportion of 515% of the weight of the cellulose.

2. Process for the production of cellulose acetate, comprising pretreating cellulose with Furthermore such prelower aliphatic acids and acetylating them by means of acetic anhydride in presence of antimony pentachloride.

3. Process for the production of cellulose acetate, comprising pretreating cellulose with lower aliphatic acids and acetylating them by means of acetic anhydride in presence of antimony pentachloride and of hydrochloric acid.

4. Process for the production of cellulose acetate, comprising pretreating cellulose with:

formic acid and acetylating them by means of acetic anhydride in presence of antimony pentachloride and of hydrochloric acid each in a proportion of 5.15% of the weight of the cellulose and in presence of a solvent for the acetate produced.

' HENRY DREYFUS. 

